How Digestive Enzymes Work on Food

The digestive system.
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The nutrients you need for good health are locked away in the foods you eat so it's your digestive system's job to set them free. By the process of digestion, food is broken down into tiny little bits so the nutrients can be released and absorbed through the walls of the small intestine.

It would take a very long time for the food just to fall apart on its own, so special digestive enzymes are necessary to speed up the process.

These enzymes don't just attack all food; they're actually quite specialized. Some go after carbohydrates, some break fats down, and others break proteins apart. -- each enzyme has a specific action.

Most enzymes are released and work in your small intestine, but a few of them are released from glands in your mouth and stomach.

Here are the main digestive enzymes, where they're made, and what they do:

Salivary amylase. Made and released by salivary glands in your mouth. Salivary amylase breaks starch down into shorter chains of glucose molecules. It works in the mouth, but once food reaches your stomach, the acidic pH deactivates it.

Lingual lipase. Made by serous glands in your tongue and the back of your mouth. Lingual lipase works in the mouth and the stomach. It breaks medium and long-chain triacylglycerols (fats) into smaller bits.

Pepsin. The primary digestive enzyme in the stomach. Chief cells in the stomach make pepsinogen, which is converted to pepsin by the acid environment of the stomach.

Pepsin breaks proteins down into polypeptides and amino acids.

Gastric lipase. Another digestive enzyme made by the stomach. It's similar to lingual lipase, but it breaks down short and medium chain triacylglycerols. Lingual and gastric lipase are most important during infancy because they break down the fats found in mother's milk.

Pancreatic amylase. This enzyme is made by the pancreas and secreted into the small intestine. Pancreatic amylase breaks starches into short chains of glucose and maltose.

Pancreatic lipase. Another pancreatic enzyme made and secreted into the small intestine. Pancreatic lipase breaks triacylglycerols into diacylglycerols, monoacylglycerols, and free fatty acids and glycerol.

Trypsin and chymotrypsin. These two pancreatic enzymes break down proteins. They break proteins and polypeptides into shorter polypeptides.

Peptidases. These enzymes are mostly made in the small intestine, except for one (carboxypeptidase), which is also made by the pancreas. The peptidases work in the small intestine and pick up where the trypsins and pepsin left off to reduce polypeptides to individual amino acids.

Sugar Enzymes. These four enzymes are all made and released by cells in the lining of the small intestine. Each enzyme works on a different type of sugar:

  • Sucrase. Breaks sucrose (table sugar) into glucose and fructose.
  • Lactase. This one breaks lactose (milk sugar) down into glucose and galactose.
  • Maltase. Breaks maltose into glucose.
  • Dextrinase. Breaks chains of glucose into individual glucose units.

Sources:

Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Sixth Edition. Belmont, CA. Wadsworth Publishing Company, 2013. Accessed February 16, 2016.

Smolin LA, Grosvenor, MB. "Nutrition: Science and Applications." Third Edition. Wiley Publishing Company, 2013. Accessed February 16, 2016. 

United States Department of Health and Human Services, National Digestive Diseases 
Information Clearinghouse (NDDIC). "Your Digestive System and How It Works." Accessed February 16, 2016. http://www.niddk.nih.gov/health-information/health-topics/Anatomy/your-digestive-system/Pages/anatomy.aspx.

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